This invention relates generally to the field of musical instruments, more particularly to a capacitive electric musical instrument vibration transducers better adapted to interface acoustic musical instruments with electronic recording and amplification equipment. (A musical instrument vibration transducer is sometimes referred to as a pickup, but that term will not be used to refer to the invention presented here to avoid confusion with electric guitar pickups and similar devices which, unlike this invention, are magnetic in nature.) There are three different general categories of musical instruments in common usage at the time of this writing: acoustic, electronic and electric. This invention relates to the first category, and aims to give acoustic instruments many of the advantages of the other instrument types. For completeness, all three categories will be discussed here.
Note that the primary emphasis of the discussion will be on percussion instruments, although this invention can be used on other types of instruments as well, including those that use some form of soundboard for sound propagation. These two categories of instruments have much in common; a percussion instrument can be understood as a soundboard stimulated by direct impact, and a banjo (a soundboard-instrument) uses a membrane as its soundboard that is essentially a drumhead in terms of its construction and mounting. In discussing the three general types of instruments, we will examine percussion instruments first, then examine the similarities between the percussion and soundboard instruments.
Acoustic percussion instruments include a number of different types of drums (such as snare, tom, bass, conga, djembe, etc.) as well as cymbals (such as hi-hat, crash, ride, gong, etc). Acoustic percussion instruments can be widely varied, such as temple blocks and cowbells, but drums and cymbals are of particular interest to musicians. Usually a number of acoustic percussion instruments are placed together in sets to be used by a single musician. Such sets of instruments are often known as drumsets, and the musician playing them known as a percussionist or drummer.
Drums typically consist of a shell (a hollow open-ended cylinder made of materials such as wood, metal, and plastic) capped on one or both ends by a drumhead (a thin, flexible disc made of materials such as plastic or animal hide). Drumheads are typically held in place by metal hoops that are secured to the shell by tension rods screwed into metal lugs. Acoustic drums are played by striking one or both heads with hands, sticks, brushes, beaters, rods, and other such devices.
Acoustic cymbals are typically discs made of metals such as bronze or brass, often mounted on stands by holes in their centers. Cymbals can also be mounted on their perimeter (like gongs). They have been carefully machined and hammered to provide certain sounds in response to activating actions, for example when played by devices such as sticks, mallets, brushes, rods, or bows, or when brought into rapid contact with one another (as in the case with hi-hat cymbals).
Acoustic percussion instruments generally interface with electronic recording and amplification systems through microphones. There are two different techniques used to record percussion sounds: close miking, where one or more microphones are placed close to each percussion instrument to capture their sounds individually, and distance miking, where fewer microphones are placed further away from the set of instruments to capture their sounds collectively.
Close miking is often more desirable because it captures individual instrument sounds more accurately, which allows more precise mixing of percussion sounds in production. It is also more complicated, due to the number of microphones needed. In close miking double-headed drums like snare drums, for example, two microphones are needed for each drum, one for each drumhead. Close miking can be very costly, especially if high quality microphones are required (as is often the case for cymbals). Distance miking is less costly and complicated, but it offers less control of instrument sounds while mixing for recording and/or amplification. Distance miking is also more likely to pick up noises from the surroundings (like other instruments, vocals, crowd noise, etc.) and make the final musical mix less clean than close miking.
A combination of close and distance miking are commonly used in live performances and recording sessions. For example, two close microphones may be used on snare drums, one for each drumhead, but only one close microphone on each tom and bass drum (even though these instruments are typically double-headed). Some loss of fidelity is experienced on toms and bass drums because the microphone only captures the sound from the head being struck, and even with close miking, the microphones can still pick up significant amounts of sound external to the drums being miked. For cymbals, one or two distant microphones are often used to capture their sounds collectively. The sounds of individual cymbals cannot be mixed individually, and other sounds (such as drum noise) are recorded as well.
Acoustic percussion instruments have a number of drawbacks. For greatest fidelity in an amplified performance or recording session, they require a large number of microphones, which can be quite expensive. Arranging these microphones requires great expertise, and can be quite time consuming. The fact that microphones can pick up significant amounts of external noise, such as other musical instruments or squeaking from a poorly lubricated bass drum pedal, can cause significant problems for sound engineers and percussionists. Another problem with acoustic instruments is that they can be very loud, often too loud for other musicians performing with a percussionist, or for neighbors of a percussionist practicing at home. Elaborate muting systems have been devised, such as erecting Plexiglas shields around drumsets or drumhead muffling systems like the invention of Suenaga, but these often change the sound of the instruments to an unacceptable degree. Using less force to play the instrument changes the playability of the instruments as well as their acoustic output, and is generally not a viable solution for volume problems.
Other acoustic musical instruments exist that propagate sound through a soundboard or its equivalent, which are referred to here collectively as soundboard instruments. These instruments include a number of stringed instruments like banjos, acoustic guitars, violins, lutes, mandolins, pianos, harps, and many others. These instruments may have a part of the instrument formally known as a soundboard, as the piano does, but many of these instruments use other parts of the instrument instead as a soundboard equivalent, such as the hollow body of an acoustic guitar or violin. In these instruments, vibrations are created in the soundboard or equivalent indirectly, generally by plucking, picking, hammering, or otherwise stimulating stretched strings attached to the soundboard or equivalent. The vibrating strings vibrate the soundboard or equivalent, which propagates the sound to the air more effectively than the vibrating strings do themselves. The banjo is particularly interesting in the context of this discussion because in terms of its construction, it is essentially a drum whose head, called a membrane, vibrates not by direct impact, but instead by the vibrations of stretched strings connected to the membrane through a bridge.
Soundboard instruments, like the acoustic percussion instruments discussed earlier, generally rely on microphones to interface with audio recording and amplification equipment. For this reason they suffer the same kinds of drawbacks that acoustic percussion instruments do. Piezoelectric devices known as contact pickups are sometimes used to sense vibrations over small areas of soundboards or their equivalents. The signal quality produced by contact pickups is generally poor, especially in terms of their low frequency response.
There are many examples of electronic percussion instruments, including the inventions of Mori et al. and Ebihara et al. These instruments do not produce musical sound directly, as acoustic instruments do. Instead, they use an electronic device (commonly referred to as a drum module) to produce electronic waveforms. These waveforms can be recordings of acoustic percussion instruments, recordings of other instrument sounds, or completely artificial waveforms produced by a synthesizer or other electronic device. These waveforms can be captured by recording or amplification equipment as if they were actual sounds captured by microphones.
Drum modules do not require a percussionist or drummer for operation. They can be operated through computer interfaces, electronic musical keyboards, or other electronic devices, although percussionists are frequently used. To simulate the instrument layout and feel of acoustic percussion instruments, a number of drum pads are typically employed. Drum pads typically feature a rubber or mesh head that can be played in a similar manner as a drumhead or cymbal, and are placed on stands around the drummer to simulate acoustic instrument placement conventions. The pads feature electronic mechanisms, typically called triggers, that sense vibrations on the pads consistent with the impact of sticks, hands, beaters, and such, and then send signals to the drum module to indicate that a particular waveform should then be emitted. Pads can feature multiple triggers to better simulate acoustic instrument behavior. For example, a pad meant to imitate a snare drum (like the one shown by Yoshino) might have two sensors, one in the center of the pad and one on the edge, which would allow the module to play ordinary drum beats, rim shots, and rim knocks depending on the signal received from the pad's multiple sensors. Triggers can also be impact sensitive, like the pressure transducer of Duncan et al., allowing drummers some measure of volume control.
Electronic drums are desirable for a number of reasons. They are much easier to set up than acoustic instruments because they don't need microphones. Drum sounds are sent directly from the drum module to recording or amplification equipment. They can play sounds that acoustic percussion instruments are physically incapable of producing. Also, electronic instruments can be played much more quietly than acoustic instruments. Because the sound produced by a drum module has nothing to do with the actual modes of vibration on the pads, electronic pads are generally made of materials that create little noise when struck, like rubber or taut nylon mesh.
Electronic percussion instruments have a number of drawbacks that make them unacceptable to large numbers of musicians. First and foremost, they lack the range and depth of acoustic instruments. The sound an acoustic instrument makes is unique every time it is played, because of factors such as instrument tuning, strike location, and so on. An electronic drum, on the other hand, generates an identically shaped waveform every time it is played. This repetitiveness can be unpleasant to many listeners. Adding extra triggers to pads (as Yoshino shows to allow triggering of rim shots), or making them pressure sensitive to change the volume at various times (as Duncan et al. shows), does little to alleviate this problem. Electronic percussion instruments also often lack the physical response characteristics (or “feel”) of their acoustic counterparts, which can limit their playability.
The trigger mechanisms for electronic percussion instruments, including the inventions of Bozzio, Duncan et al., and others, have received much attention. It should be noted that these triggers, often known as drum pads, pressure transducers, piezoelectric pickups, and other similar names, are not used for the same purpose as microphones or magnetic pickups. When played, drum triggers produce a signal that triggers the drum module or equivalent to play a sound; they do not produce a microphone-like or magnetic pickup-like signal directly. The signal they produce is not intended to reproduce the sound of the triggering mechanism itself. For example, the invention of Duncan et al. is a pressure transducer that produces a non-oscillatory signal indicating the amount of pressure being applied to the triggering device by the percussionist as a function of time. These devices cannot be used without a drum module, synthesizer, or other such device, and are incapable of reproducing the (often undesirable) exact sound being emitted from the triggering device as a result of the triggering strike.
Soundboard instruments have their electronic counterparts as well, such as the electronic keyboard and (more rarely) electronic guitar-like devices. Again, they have an interface similar to their acoustic counterparts, but their output waveforms are based on sampled or electronically synthesized sounds from an electronic module within the instrument. They are often rejected by musicians and listeners for the same reasons electronic percussion instruments are rejected, including their repetitive output waveforms and their poor playability compared to their acoustic counterparts.
Acoustic musical instruments often have purely electric analogs, the most famous and commonly used being stringed instruments like electric guitars and basses, which use magnetic pickups (the invention of Fender is one example) to transduce metallic string vibrations into electric signals. Other electric analogs of soundboard instruments exist, such as electric violins, that use transducers (most commonly piezoelectric elements) on variants of the instrument bridge to detect string vibrations (as opposed to vibrations of an instrument's soundboard or other vibrating surfaces that actually produce the sound of the instrument), a combination which is often referred to as a saddle transducer. Ashworth-Jones, Carman et al., Benioff, and Evans all show examples of this general type of transducer. Neither magnetic pickups nor saddle transducers capture the vibrations of a soundboard or its equivalent; in fact, instruments with these kinds of transducers often lack a soundboard or equivalent entirely, and emit little sound directly. Consequently, electric stringed instruments do not sound like their acoustic counterparts, but instead have their own unique sounds. These electric instruments are used and valued for many reasons, but they are no substitute for their acoustic progenitors. Acoustic guitars and violins, for example, are still commonly found on concert stages and in recording studios for this reason.
Similarly, electric percussion instruments attempt to combine the playability and uniqueness of acoustic instruments with the implementation simplicity of electronic instruments. In a short analogy, an electric percussion instrument is to percussion what an electric guitar is to guitars. Various models have been proposed, although none of them appear to be in widespread use at the time of this writing.
Some models, such as the invention of Rogers, use a conventional acoustic drumhead with a magnetic speaker cone placed underneath, which is wired to act as a microphone. These systems do not have the dynamic range of an ordinary microphone. Furthermore, the speaker cones tend to be so large that they cannot be used in double-headed drums, because they disrupt the sound waves inside drums to an unacceptable degree. It should also be noted that speakers can be quite heavy; acoustic drumsets are already heavy and bulky, so adding a heavy speaker-like microphone is undesirable.
Other proposed models, such as the invention of Green, involve magnetic pickups (magnets and coils of wire which detect changes in the magnet's position) to capture drumhead or cymbal vibrations. Pickup-based systems are at a disadvantage because they require special drumheads or cymbals that do not well emulate traditional acoustic drumheads or cymbals. Furthermore, the magnetic pickups tend to capture vibrations at a single point only, rather than sample the vibrational state of an entire cymbal or drumhead, as the sound from an acoustic instrument does. Furthermore, a single pickup is often very dense compared to a drumhead or cymbal. Placing a single pickup on a drumhead breaks the vibrational symmetry of the head, which tends to create a vibrational node (or dead spot) at that point. The single pickup can thus destroy the vibrational fidelity of a drumhead. The vibration of a whole drumhead or cymbal requires an impractical and costly number of pickups, as well as a complicated mixing apparatus.